2008 Sprinter 300 kbs

[NurseSteve]

I am confused which of these valves is the REAL black water valve. I know this question may sound silly but I would like confirmation. I am new trailer owner of this beautifully well kept trailer and not sure which is which. I would like to know what the three values are each responsible for.
Starting from left to right
Valve 1 grey water?
Value 2 black water?
Valve 3 I have no idea??
Help.... I need some guidance

TIA

[chuckster57]

Valve 1- is 1 1/2” making it a gray water valve
Valve 2- is 1 1/2” making it a gray water valve
Valve 3-is underneath the coroplast with a pull handle so I’d say it’s the black waste valve 3”

[Canonman]

The smaller lines and gate valves 1 &2 should both be gray water based on their size. There should be another valve for your larger line which again by it's size should be the black tank drain. Possible #3 goes further back in the underbelly to the black tank valve.
Run some water to your galley tank and the bathroom sink tank with some different colored food coloring. Open #1 and see what color. The same with #2. Wait to check #3 until you are hooked up to the sewer if not already. Then give #3 a pull. Make sure you have water in each of the tanks sufficient to test. 3 or 4 gallons should do it.